1. Field of the Invention
The present invention relates to a mobile communication system, a mobile terminal, a transfer device, and a mobile communication method.
2. Description of the Related Art
In a conventional mobile communication system, a base station conducts both connection management when a mobile terminal connects to the base station, and mobility management for ensuring mobility of a mobile terminal such as buffering and transfer of packets. Therefore, the base station and mobile terminal are designed and managed so that connection management and mobility management may coexist and be optimized.
Furthermore, in recent years, a mobility management scheme called HMIP (Hierarchical Mobile IPv6) is under consideration In HMIP, an access router for conducting connection management and a mobility anchor point for conducting mobility management are placed at different sites rather than at one site. Therefore, a mobile terminal needs to grasp a mobility anchor point used for mobility management. Accordingly, in an access router, the addresses of mobility anchor points in the neighborhood of the access router are previously set. Further, the mobile terminal is notified by the access router connected thereto of the preset address of the mobility anchor point, and thereby grasps the mobility anchor point.
However, in the case where a base station conducts both connection management and mobility management, a connection management service and a mobility management service are provided in an integrated manner. Also in HMIP in which an access router for conducting connection management and a mobility anchor point for conducting mobility management are placed at different sites, since the address of a mobility anchor point needs to be set in the access router, a connection management service and a mobility management service are provided in an integrated manner.
As a result, a user of the mobile terminal has a problem of small flexibility to select a service, because the user must always use the connection management service and mobility management service as a set. Furthermore, a communications carrier that provides services to mobile terminals has also a problem of failing to sufficiently acquire users of the mobility management service, because it can provide the mobility management service only to the users who use the connection management service it provides.
Furthermore, in the case where one attempts to provide a connection management service and a mobility management service separately, the following new problem occurs. Since an access router for providing a connection management service and a mobility anchor point for providing a mobility management service are separately placed and controlled, the address of the mobility anchor point cannot be previously set in the access router. As a result, a mobile terminal cannot be notified the address of the mobility anchor point by the access router. Therefore, the mobile terminal must be able to grasp a transfer device such as a mobility anchor point by itself. Furthermore, the mobility anchor point cannot also cause the access router to notify the mobile terminal of the address of the mobility anchor point. Therefore, a transfer device such as a mobility anchor point must be able to make the existence of the mobility anchor point known to a mobile terminal by itself.
Furthermore, a transfer device for conducting mobility management such as a mobility anchor point must be able to provide a mobility management service such as transfer of packets only to the mobile terminals used by subscribers of the mobility management service.